1. Field
The present invention relates generally to particle accelerators. More particularly, embodiments of the present invention relate to particle accelerators designed to output particles at various energies.
2. Description
A particle accelerator produces charged particles having particular energies. In one common application, a particle accelerator produces a radiation beam used for medical radiation therapy. The beam may be directed toward a target area of a patient in order to destroy cells within the target area.
A conventional particle accelerator includes a particle source, an accelerator waveguide and a microwave power source. The particle source may comprise an electron gun that generates and transmits electrons to the waveguide. The waveguide receives electromagnetic waves from the microwave power source, which may comprise as a magnetron or a klystron. The electrons are accelerated through the waveguide by oscillations of the electromagnetic waves within cavities of the waveguide.
The accelerating portion of the waveguide includes cavities that are designed to ensure synchrony between electrons received from the particle source and the oscillating electromagnetic wave received from the microwave power source. More particularly, the cavities are carefully designed and fabricated so that electric currents flowing on their surfaces generate electric fields that are suitable to accelerate the electron bunches. The oscillation of these electric fields within each cavity is delayed with respect to an upstream cavity so that a particle is further accelerated as it arrives at each cavity.
A particle accelerator is usually designed to output particles within a limited range of output energies. Due to the number of factors that interact during operation, a conventional particle accelerator cannot efficiently provide particle energies outside of this small window. As described above, these interacting factors include, but are not limited to: the magnitude of an electron current produced by the particle source; the frequency and energy of the electromagnetic wave; shape, the construction and resonant frequency of the accelerator waveguide cavities; and the desired output energy.
Some conventional particle accelerators attempt to efficiently output particles having widely-varying energies. One system uses a shunt to “short out” a portion of the accelerator waveguide and to therefore reduce particle acceleration based on a desired output energy. Another system includes two separate waveguide sections with RF phase adjustment for selectively accelerating electrons based on a desired output energy. Neither of these current accelerator structures is seen to provide efficient operation at substantially different output energies.